3: Ecology

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Melissa Ha and Rachel Schleiger
Yuba College & Butte College via ASCCC Open Educational Resources Initiative

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Ecology is the study of the interactions of living organisms with their environment. One core goal of ecology is to understand the distribution and abundance of living things in the physical environment. Attainment of this goal requires the integration of scientific disciplines inside and outside of biology, such as biochemistry, physiology, evolution, biodiversity, molecular biology, geology, and climatology. Some ecological research also applies aspects of chemistry and physics, and it frequently uses mathematical models.

Why study ecology? Perhaps you are interested in learning about the natural world and how living things have adapted to the physical conditions of their environment. Or, perhaps you’re a future physician seeking to understand the connection between human health and ecology.

Humans are a part of the ecological landscape, and human health is one important part of human interaction with our physical and living environment. Lyme disease, for instance, serves as one modern-day example of the connection between our health and the natural world. More formally known as Lyme borreliosis, Lyme disease is a bacterial infection that can be transmitted to humans when they are bitten by the deer tick (Ixodes scapularis), which is the primary vector for this disease (figure \(\PageIndex{a}\)). However, not all deer ticks carry the bacteria that will cause Lyme disease in humans, and I. scapularis can have other hosts besides deer. In fact, it turns out that the probability of infection depends on the type of host upon which the tick develops: a higher proportion of ticks that live on white-footed mice carry the bacterium than do ticks that live on deer. Knowledge about the environments and population densities in which the host species is abundant would help a physician or an epidemiologist better understand how Lyme disease is transmitted and how its incidence could be reduced.

Photo (a) shows a deer tick on a leaf. The tick has a brown oval body with a smaller, round oval toward the front. The head and legs are black. Photo (b) shows an arm with a red, circular rash enclosed in a ring-like rash. Photo (c) shows a brown mouse with a white belly and legs and large, round ears. — Figure \(\PageIndex{a}\): The (a) deer tick carries the bacterium that produces Lyme disease in humans, often evident in (b) a symptomatic bull’s eye rash. The (c) white-footed mouse is one well-known host to deer ticks carrying the Lyme disease bacterium. (credit a: modification of work by Scott Bauer, USDA ARS; credit b: modification of work by James Gathany, CDC; credit c: modification of work by Rob Ireton)

Ecologists ask questions across four levels of biological organization—organismal, population, community, and ecosystem. At the organismal level, ecologists study individual organisms and how they interact with their environments. At the population and community levels, ecologists explore, respectively, how a population of organisms changes over time and the ways in which that population interacts with other species in the community. Ecologists studying an ecosystem examine the living species (the biotic components) of the ecosystem as well as the nonliving portions (the abiotic components), such as air, water, and soil, of the environment. The objective of this unit will be to further explore these topics and how they connect to and overlap with environmental science.

Attribution

Modified by Melissa Ha and Rachel Schleiger from Ecology and the Biosphere by OpenStax (licensed under CC-BY)

3.1: Ecology Overview
Ecology can be studied at the organismal, population, community, and ecosystem levels.
3.2: Populations
Populations are interacting and interbreeding groups of individuals from the same species in a common area. The study of population ecology explores how individuals in a population are distributed over space, the factors that regulate population growth, and life history traits, which relate to lifespan and reproduction.
3.3: Communities
Communities consist of multiple interacting populations (of different species) in a common area. The study of communities focuses on how organisms interact with each other, trophic structure (food chains and food webs), and the stability of community structure.
3.4: Ecosystems
Ecosystems consist of biotic (living) and abiotic (non-living) components interacting together. Ecosystems may be freshwater, marine, or terrestrial. Biogeochemical cycles describe the movement of chemical elements through different ecosystem components. Soils are one of these components, and they are critical in determining plant distribution and abundance.
3.5: Biomes
Biomes are large geographical areas characterized by vegetation and climate, including temperature and precipitation. Temperature decreases with latitude and altitude. Precipitation is high at the equator and low at 30 degrees N and S. Terrestrial biomes are found on land, while aquatic biomes are found in water.

Thumbnail image - "Orchid mantis" is in the Public Domain

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